Ultra-thin precision stainless steel foil with high strength and high plasticity and production method thereof

ABSTRACT

A method for producing a stainless steel foil comprises the following steps: rolling a raw material steel coil in an intermediate rolling process comprising three rolling processes; rolling the finished product in the rolling process; annealing and straightening the finished product. The application also provides a stainless steel foil prepared by the method. The method can solve the defect that the high strength and high plasticity of the ultra-thin stainless steel foil are difficult to meet at the same time.

TECHNICAL FIELD

The application relates to the technical field of production andmanufacture of ultra-thin precision stainless steel strips, inparticular to an ultra-thin precision stainless steel foil with highstrength and high plasticity and a production method thereof.

BACKGROUND

At present, the ultra-thin precision stainless steel strip has beenapplied in the fields of aerospace, petrochemical industry, medicalelectronics, communication semiconductors, auto parts, computerproducts, etc., and has a very high added value, which puts forwardhigher requirements for the metal characteristics, corrosion resistanceand surface quality of stainless steel. Especially, for the precisionstainless steel foil products with ac high strength with a width of morethan 600 mm, a thickness of less than 0.05 mm and an elongation of atleast 50%, there is no technology to produce such products at present.At present, only a few enterprises in Japan and the United States canproduce stainless steel foil products with a thickness of 0.05 mm, butthe width is limited, and only products with a width of less than 450 mmcan be produced, and the elongation of the foil is less than 50%.

On the one hand, there is a great demand for high-performance stainlesssteel foil in the market, but on the other hand, there is currently alack of rolling technology for precision stainless steel foils with awidth exceeding 600 mm. Therefore, developing a high-strength andhigh-plasticity precision stainless steel foil with a width of more than600 mm and a thickness of less than 0.05 mm to fill the technical gapand meet the market demand has become an urgent technical problem forthose skilled in the art.

SUMMARY

In order to solve all or part of the above problems, the purpose of thepresent application is to provide a production method of an ultra-thinprecision stainless steel foil with high strength and high plasticityand the ultra-thin precision stainless steel foil with high strength andhigh plasticity prepared by the production method.

Specifically, the application is realized by the following technicalsolution:

A method for producing a stainless steel foil which includes thefollowing steps of:

S1, rolling a raw material steel coil in an intermediate rolling processcomprising three rolling processes;

S2, rolling a finished product in a rolling process;

S3, carrying out annealing treatment and straightening treatment on thefinished product.

Optionally, the raw material steel coil is 301 L steel coil.

Optionally, the intermediate rolling process includes a first rollingprocess with a deformation of 45%˜55%, a second rolling process with adeformation of 50%˜60%, and a third rolling process with a deformationof 50%˜60%, wherein high-temperature intermediate flexible brightannealing is respectively carried out immediately after the firstrolling process, the second rolling process and the third rollingprocess are completed, with an annealing temperature being 950˜1150° C.,and an annealing TV value being 2.5˜15, and TV values of the threeannealing processes are gradually reduced.

Optionally, each rolling process of the intermediate rolling processadopts five rolling passes, wherein, a high-roughness wire drawingroller is adopted in the first pass, the material of the roller is M2,the roughness Ra of the roller is 1.5˜3.0 μm, and a single passdeformation is 23%˜28%; rollers with a roughness Ra of 0.1˜0.5 μm areadopted for the remaining passes.

Optionally, the finished product rolling process sequentially comprises:a first rolling pass with a deformation of 25%˜30%; a second rollingpass with deformation of 20%˜28%; a third rolling pass with deformationof 15%˜20%; a fourth rolling pass with a deformation of 5%˜10%; wherein,after finishing the third rolling pass, a TA stress relieving heattreatment is carried out at 600˜800° C. and a TV value is not less than1, and then the fourth rolling pass is carried out.

Optionally, the rolling tension is 230˜300 N/mm² and the rolling forceis ≤500 KN in the finished product rolling process.

Optionally, for a work roller used in the finished product rollingprocess, the diameter is Φ20˜30 mm, the material is M2, the roughness Rais 0.1˜0.25 μm, and the surface hardness is HRC 63˜68.

Optionally, an annealing temperature of the finished product is900˜1100° C.

Optionally, the straightening treatment adopts 23-rollers stretch-bendstraightening, with an opening degree of −1.5˜−2.0 mm and an elongationof 0.3%˜0.45%, and a diameter of a straightening roller is 12˜16 mm.

A stainless steel foil obtained by the above-mentioned method forproducing a stainless steel foil, wherein the stainless steel foil has athickness of ≤0.05 mm, a width of ≥600 mm, a tensile strength of ≥650Mpa, and an elongation of ≥50%.

Compared with the prior art, the ultra-thin precision stainless steelfoil with high strength and high plasticity and the production methodthereof have at least the following beneficial effects:

In the step of selecting a raw material, raw materials are selectedthrough the comparative analysis of strength and elongation after heattreatment. In the production process and the intermediate annealinggrain structure design step, the flexible annealing process design inthe intermediate rolling process is carried out, and the grains arerefined to 9˜10 grades through process innovation, thus laying afoundation for the ultra-fine grain finished products; in theintermediate rolling process and finished product rolling process, a newdesign of TA stress relieving process is provided so that thedeformation of the finished product rolling process is more sufficientand the internal organization structure is more uniform. At the sametime, process parameter optimization, pass design and rolling force andtension control for the work roller of the finished product rollingprocess are carried out. In the annealing process of the finishedproduct, the heat treatment process of rapid annealing at a lowtemperature is designed to inhibit grain growth and realize the controlof a 3˜5 m ultra-fine grain structure. In the straightening and levelingprocess, a 23-rollers stretch-bend straightening process is designed,with an opening degree of −1.5˜−2.0 mm and an elongation of 0.3%˜0.45%.Therefore, the production process of the ultra-thin precision stainlesssteel foil with high strength and high plasticity with a thickness ofless than 0.05 mm is realized, and the surface quality of the steelstrip is good, and the performance is uniform and stable, thus meetingthe demand of high quality.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a process flow chart of the production method of theultra-thin precision stainless steel foil with high strength and highplasticity according to the present application.

FIG. 2 is a schematic diagram of a work roller used in finished productrolling process according to one embodiment of the present application.

FIG. 3 is a diagram of the roller system of the SUNDWIG 4-column 20-highreversible rolling mill.

DESCRIPTION OF EMBODIMENTS

In order to fully understand the purpose, characteristics and efficacyof the present application, the present application will be described indetail through the following specific embodiments. Except for thefollowing contents, the process method of the application adoptsconventional methods or devices in the field. Unless otherwise stated,the following terms have the meanings commonly understood by thoseskilled in the art.

As far as stainless steel strip is concerned, the strength of thematerial will increase while the plasticity of the material willdecrease under the conventional process, and there is a bigcontradiction between plasticity and strength. Taking austeniticstainless steel as an example, its strength exceeds 700 MPa, and itsplasticity (usually measured by elongation) is lower than 50%.Conventionally, the method of obtaining a high strength is mainlythrough a certain proportion of work hardening, which will directly leadto a sharp decline in plasticity. At present, the conventional processcannot achieve high strength and high plasticity at the same time.

Aiming at the problem that the wide and ultra-thin precision stainlesssteel foil cannot have high strength and high plasticity at the sametime at present, the inventor of the present application creativelyimproves the process through research, thus proposing a productionmethod of the ultra-thin precision stainless steel foil with highstrength and high plasticity. The method can realize that refinement ofthe internal organizational structure, thereby improve the strength ofthe material on the basis of ensure the plasticity of the strip.

The production method of the ultra-thin precision stainless steel foilwith high strength and high plasticity includes the following steps of:rolling a raw material steel coil in an intermediate rolling processcomprising three rolling processes; finished product rolling process;and, carrying out annealing treatment and straightening treatment on thefinished product.

According to the application, the process flow of three rollingprocesses−intermediate flexible annealing−large deformation rolling in afinished product rolling processes+process TA heat treatment−finishedproduct rapid annealing at a low temperature, is adopted, and theproduction of a stainless steel foil with a thickness ≤0.05 mm, a width≥600 mm, a tensile strength ≥650 MPa and an elongation ≥50% is realized.

FIG. 1 shows the process flow chart of the production method ofultra-thin precision stainless steel foil with high strength and highplasticity. With reference to FIG. 1, the production method of theultra-thin precision stainless steel foil with high strength and highplasticity of the present application will be described in detail below.

The production method of the ultra-thin precision stainless steel foilwith high strength and high plasticity can be applied to raw steel coilsof any brand. In the implementation process, in order to achieve thebest effect, a preparation step, i.e., step S0 of selecting a rawmaterial steel coil, is performed before the method of the presentapplication is executed.

In the step S0, the rolling raw materials most suitable for theproduction method of the present application are selected by analyzingthe rolling properties and representative compositions of raw materialsof different materials after heat treatment.

According to the research of the inventor, the production method of theapplication preferably adopts 301 L (Chinese National standard brand)steel coil as the raw material.

Taking 301 L as an example, through the analysis of rolling and heattreatment of different materials, it can be seen that with the reductionof C content, the strength of 301 L decreases slightly, but theelongation is relatively high when the deformation is 50%. Under thecondition of the same deformation, the rolling deformation resistance ofthe 301 L steel is small, and its plastic toughness is strong, which isbeneficial to the production of rolling and heat treatment processes.Therefore, 301 L is selected as the raw material of the productionmethod of the present application.

Preferably, in order to ensure various performance indexes and plateshape of the stainless steel foil obtained by the production method ofthe present application, the thickness of the raw steel coil is ≥0.5 mm(preferably 0.5˜1.0 mm), the width is 500˜650 mm, and the surface finishis 2B (matte surface, GB/T 3280).

Subsequently, the production method of the stainless steel foil of thepresent application is started, including:

S1, rolling the raw material steel coil in an intermediate rollingprocess.

The intermediate rolling process includes three rolling processes: afirst rolling process with a deformation of 45%˜55%; a second rollingprocess with a deformation of 50%˜60%; a third rolling process with adeformation of 50%˜60%. After the completion of the first rollingprocess, the second rolling process and the third rolling process,high-temperature intermediate flexible bright annealing is carried outat 950˜1150° C., and the annealing TV value (that is, the product of thethickness of the steel coil and the running speed of the steel coil) is2.5˜15. Moreover, the TV value of the third annealing is graduallyreduced, thus ensuring the grain structure refinement after intermediateannealing.

Five rolling passes are adopted for each rolling process. Among them,the first pass adopts high-roughness wire drawing roller, the materialof the roller is M2 (namely molybdenum high speed steel), the roughnessRa of the roller is 1.5˜3.0 m, the single pass deformation is 23%˜28%,the remaining passes adopt conventional rollers with the roughness Ra of0.1˜0.5 m, and the single pass deformation of the remaining four passesis gradually reduced to ensure the overall deformation.

Through the process of“rolling-annealing-rolling-annealing-rolling-annealing”, the totaldeformation of the intermediate rolling process can reach 87.5%˜93%,which ensures sufficient deformation of the original structure of thestrip. Through three times of rapid annealing at a high temperature, theinternal grain coarseness is suppressed, and the size and uniformity ofthe internal structure grain are adjusted. After the internal grains arerefined to 9˜10 grades, it will provide good machinability for therolling of the finished product with a deformation above 60% grade. Ifthe grain structure is below grade 9, especially below grade 7, themachinability of the material will not meet the requirements of largedeformations in the rolling of the finished product, and problems suchas strip breakage may occur. After three times of “rolling-annealing”design, the internal uniformity of the strip can be guaranteed, and atthe same time, the possibility of a uniform deformation of the strip isprovided. In the first pass of each rolling process, the roughness Ra is1.5˜3.0 μm, and the single pass deformation is 23%˜28%, so as to ensurethe rapid microstructure transformation in the rolling process.

S2, finished product rolling process.

In step S2, the diameter of the work roller used for rolling is Φ20˜30mm, the material of the work roller is M2 (namely molybdenum high-speedsteel), the roughness Ra of the work roller is 0.1˜0.25 μm, and thesurface hardness of the work roller reaches HRC 63˜68. As a specificexample, as shown in FIG. 2, the work roller used in step S2 has alength of, for example, 780 mm, and the supporting sections at both endsare, for example, 110 mm each.

The finished product rolling process of step S2 is divided into fourrolling passes, and the deformation of each pass is gradually reduced.Specifically, in the first rolling pass, the deformation is 25%˜30%; inthe second rolling pass, the deformation is 20%˜28%; in the thirdrolling pass, the deformation is 15%˜20%; in the fourth rolling pass,the deformation is 5%˜10%. Preferably, after finishing the third rollingpass, TA stress relieving heat treatment (i.e., tension low-temperaturestress-relieving heat treatment) is carried out at a temperature of600˜800° C. and a TV value of not more than 1, and then the fourthrolling pass is carried out.

In step S2, the rolling tension of the finished product is controlled at230˜300 N/mm², and the rolling force is controlled below 500 KN.

In step S2, a TA stress relieving process is added to ensure that theinternal stress of the strip is eliminated under the condition of largedeformation in the first three passes, reduce the deformation resistancein the last pass, and improve the rolling dimensional accuracy androlling plate shape of the finished product, thereby achieving more than60% of the rolling deformation of the finished product, making theorganizational structure more fragmented, ensuring more nucleationpoints in the solid solution process during the heat treatment of thefinished product, and thus refining the grains, which is the basis ofthe finished product 3˜4 m grain structure. After TA stress relievingtreatment, the internal deformation resistance of the strip is reduced,which greatly promotes the stable control of rolling force and tensionin the last pass and ensures the refinement of the internal structure ofthe strip.

S3, carrying out annealing treatment and straightening treatment on thefinished product.

After the finished product rolling process, the steel foil is annealedat a low temperature of 900˜1100° C. with a TV value of not less than 2.By rapid annealing at low temperature, the grain growth is restrainedand the microstructure of 3˜5 m ultrafine grains is controlled.

After annealing, straightening and leveling are carried out. 23-rollersstretch-bend straightening process is adopted, the opening degree is−1.5˜−2.0 mm, the elongation is 0.3%˜0.45%, and the roller diameter ofstraightening roller is 12˜16 mm.

The production method of the application can be carried out by adoptinga SUNDWIG 4-column 20-high reversible rolling mill. FIG. 3 shows theroller system diagram of SUNDWIG 4-column 20-high reversible rollingmill, which is mainly composed of a pair of work rollers 1, two pairs offirst intermediate rollers 2, three pairs of second intermediate rollers3 and four sets of backing bearings 4. The unique 4-column framestructure of the rolling mill makes it possible to adopt inclinedrolling according to the actual situation of the coil in the rollingprocess, thus ensuring good coil shape and reducing the fluctuation ofthe coil shape in the rolling process. Of course, this is only anexample, and the method of the present application can also beimplemented by other rolling mills.

The above-mentioned production method can solve the contradictionbetween high strength and high plasticity, realize the bidirectionalregulation of high strength and high plasticity, and make the foilmaterial have good surface quality and uniform and stable performance.Particularly, the thickness of the stainless steel foil is ≤0.05 mm, thewidth is ≥600 mm, the tensile strength is ≥650 MPa, and the elongationis ≥50%.

EXAMPLES

The following examples further illustrate the present application, butdo not limit the present application to the scope of the examples. Theexperimental methods for which specific conditions are not indicated inthe following examples shall be selected according to the conventionalmethods and conditions, or according to the commodity specifications.

The following examples and comparative examples refer to GB/T228.1(Standard for Tensile Test of Metallic Materials) for testing theparameters.

The following examples and comparative examples are all carried out bySUNDWIG 4-column 20-high reversible mill of SUNDWIG, Germany.

Example 1

The method of this embodiment includes the following steps:

S0, selecting raw material steel coil: 301 L stainless steel coil with athickness of 0.5 mm×a width of 615 mm and a surface finish of 2B (matte)was selected as a rolling raw material.

S1, intermediate rolling process: the design parameters and relatedtechnical requirements of the intermediate rolling process are shown intable 1.

TABLE 1 Incoming Thick- Require- Other material ness ment for technicalthick- after annealing require- Pass ness rolling Deformationtemperature ments First 0.5 mm 0.22 mm 56.0% 1080° C., Trimming rollingTV value 8.8 before process rolling. Second 0.22 mm   0.1 mm 54.5% 1050°C., rolling TV value 4.5 process Third 0.1 mm 0.05 mm 50.0% 1000° C.,Trimming rolling TV value 2.6 before process rolling.

Five rolling passes are adopted for each rolling process, wherein, thefirst pass adopts high-roughness wire drawing roller, the rollermaterial is M2 (namely molybdenum high speed steel), the roughness Ra ofthe roller is 1.65 μm, and the single pass deformation is 25%; theremaining passes adopt conventional rollers with the roughness Ra of0.28 μm, and the single pass deformation of the remaining four passes isgradually reduced to ensure the overall deformation.

S2, finished product rolling process:

The diameter of the work roller was Φ25 mm, the material of the workroller was M2, and the roughness Ra of the work roller was 0.15 μm. Thefinished product rolling process included: a first pass, rolling from0.05 mm to 0.036 mm; a second pass, rolling from 0.036 mm to 0.027 mm; athird rolling pass, rolling from 0.027 mm to 0.022 mm; TA stressrelieving heat treatment at 720° C.; a fourth pass, rolling from 0.022mm to 0.02 mm. The design parameters and related technical requirementsof finished product rolling process are shown in Table 2:

TABLE 2 Incoming Thick- material ness thick- after Pass ness rolling.Deformation Remarks First pass  0.05 mm 0.036 mm 28% Second pass 0.036mm 0.027 mm 25% Third pass 0.027 mm 0.022 mm 18.5%   TA treatment 0.022mm Heat treatment temperature 720° C. Fourth pass 0.022 mm  0.02 mm9.1% 

The rolling tension of the finished product process was controlled at280 N/mm², and the rolling force was controlled at 450 KN.

S3, carrying out low-temperature rapid heat treatment, wherein the heattreatment temperature was 950° C., the grain size was controlled to be3˜5 μm, and the grain size of the finished product must be strictlycontrolled and detected; then 23-rollers stretch-bend straighteningtreatment was adopted, and the opening degree was −1.6 mm, theelongation was 0.45%, and the roller diameter was 12 mm.

The foil obtained in this example was tested, and the thickness of theworking side was measured to be 0.019 mm, the thickness of thetransmission side was measured to be 0.02 mm (the overall size was 0.02mm), the width was 600 mm, the tensile strength was 700 MPa, and theelongation was 50%.

Comparative Example

S0, selecting raw material steel coil: 301 L stainless steel coil with athickness of 0.35 mm×a width of 615 mm and a surface finish of 2B(matte) was selected as a rolling raw material.

S1, intermediate rolling process: the intermediate rolling process wasdesigned to include three passes, wherein the first pass was from 0.35mm to 0.15 mm, the second pass was from 0.15 mm to 0.07 mm, the thirdpass was from 0.07 mm to 0.035 mm, and the annealing temperature was1050° C.

S2, finished product rolling process: the diameter of the work rollerwas (1) 25 mm, the material of the work roller was M2, and the roughnessRa of the work roller was 0.15 m.

The finished product rolling process specifically included: rolling from0.035 mm to 0.029 mm in the first pass, rolling from 0.029 mm to 0.025mm in the second pass, rolling from 0.025 mm to 0.022 mm in the thirdpass, and rolling from 0.022 mm to 0.02 mm in the fourth pass at anannealing temperature of 1050° C. The tension was controlled at 300N/mm², and rolling force was controlled at 450 KN.

The measured thickness of the foil was 0.019 mm on the working side,0.02 mm on the transmission side, 580 mm in width, 590 MPa in tensilestrength and 40% in elongation.

The above-mentioned embodiments are preferred embodiments of the presentapplication, but the implementation of the present application is notlimited by the above-mentioned embodiments. Any other substitutions,modifications, combinations, changes, simplifications, etc. made withoutdeparting from the spirit and principles of the present applicationshall be equivalent substitutions and shall be included in the scope ofprotection of the present application.

1. A method for producing a stainless steel foil, comprising thefollowing steps of: rolling a raw material steel coil in an intermediaterolling process comprising three rolling processes; finished productrolling process; carrying out annealing treatment and straighteningtreatment on the finished product.
 2. The method for producing astainless steel foil according to claim 1, wherein the raw materialsteel coil is 301 L steel coil.
 3. The method for producing a stainlesssteel foil according to claim 1, wherein the intermediate rollingprocess comprises a first rolling process with a deformation of 45%˜55%,a second rolling process with a deformation of 50%˜60%, and a thirdrolling process with a deformation of 50%˜60%, wherein high-temperatureintermediate flexible bright annealing is respectively carried outimmediately after the first rolling process, the second rolling processand the third rolling process are completed, with an annealingtemperature being 950˜1150° C., and an annealing TV value being 2.5˜15,and TV values of the three annealing processes are gradually reduced. 4.The method for producing a stainless steel foil according to claim 3,wherein each rolling process of the intermediate rolling process adoptsfive rolling passes, wherein, a high-roughness wire drawing roller isadopted in a first pass, the material of the roller is M2, the roughnessRa of the roller is 1.5˜3.0 μm, and a single pass deformation is23%˜28%; rollers with a roughness Ra of 0.1˜0.5 μm are adopted for theremaining passes.
 5. The method for producing a stainless steel foilaccording to claim 1, wherein the finished product rolling processsequentially comprises: a first rolling pass with a deformation of25%˜30%; a second rolling pass with deformation of 20%˜28%; a thirdrolling pass with deformation of 15%˜20%; a fourth rolling pass with adeformation of 5%˜10%; wherein, after finishing the third rolling pass,a TA stress relieving heat treatment is carried out at 600˜800° C. and aTV value is not less than 1, and then the fourth rolling pass is carriedout.
 6. The method for producing a stainless steel foil according toclaim 1, wherein the rolling tension is 230˜300 N/mm² and the rollingforce is ≤500 KN in the finished product rolling process.
 7. The methodfor producing a stainless steel foil according to claim 1, wherein for awork roller used in the finished product rolling process, the diameteris φ20˜30 mm, the material is a molybdenum high speed steel, theroughness Ra is 0.1˜0.25 μm, and the surface hardness is HRC 63˜68. 8.The method for producing a stainless steel foil according to claim 1,wherein the annealing temperature of the finished product is 900˜1100°C.
 9. The method for producing a stainless steel foil according to claim1, wherein the straightening treatment adopts 23-rollers stretch-bendstraightening, with an opening degree of −1.5˜−2.0 mm and an elongationof 0.3%˜0.45%, and the diameter of the straightening roller is 12˜16 mm.10. A stainless steel foil obtained by the method for producing astainless steel foil according to claim 1, wherein the stainless steelfoil has a thickness of ≤0.05 mm, a width of ≥600 mm, a tensile strengthof ≥650 Mpa, and an elongation of ≥50%.